(a) Technical Field
The present invention relates to a pulsating operation method and system for a fuel cell system. More particularly, the present invention relates to a pulsating operation method for a fuel cell system, which smoothly discharges water remaining in a fuel electrode of a fuel cell and, at the same time, maximizes fuel utilization.
(b) Background Art
Typically, fuel cell systems include a fuel cell stack that generates electricity via an electrochemical reaction, a fuel supply system supplying hydrogen as a fuel to the fuel cell stack, an air supply system supplying oxygen-containing air as an oxidant required for the electrochemical reaction in the fuel cell stack, a thermal management system (TMS) that removes reaction heat from the fuel cell stack to the outside of the fuel cell system, controlling operation temperature of the fuel cell stack, and performing water management.
The above configuration and operation of the fuel supply system in the fuel cell system will be described with respect to FIG. 1A. Fuel supplied along a hydrogen supply line 18 from a fuel tank is fed into a fuel electrode (anode) 12 of a fuel cell through an anode inlet 14 of the fuel cell and subjected to a reaction to generate electricity, and a portion of unreacted hydrogen is discharged through an anode outlet 16.
At this time, the operating pressure of the anode of fuel cell is maintained at a predetermined pressure regardless of the operating time of the fuel cell as shown in FIG. 1B. Moreover, a portion of unreacted hydrogen discharged through an anode outlet 16 is recirculated to the anode inlet 14 by the operation of a recirculation device 20 (e.g., a recirculation blower motor) and the remaining hydrogen passes through a hydrogen purge valve 22 together with water and is discharged to the outside. As such, the recirculation device 20 is connected to the anode outlet 16 of the fuel cell such that the unreacted hydrogen remaining in the anode 12 is recirculated to the anode inlet 14 and reused for the purpose of discharging water from the anode 12.
Meanwhile, water is generated by the reaction to generate electricity and remains in a channel in the anode of the fuel cell, and the remaining water may cause corrosion of a catalyst layer that constitutes the anode of the fuel cell. Thus, the remaining water needs to be smoothly discharged. Therefore, as shown in FIG. 2A, a separate pulsation generator 24 that pulsates the operating pressure of the fuel supplied to the anode is installed at a certain position of the hydrogen supply line.
When the unreacted hydrogen is supplied again to the anode 12 of the fuel cell by the operation of the recirculation device 20, the hydrogen being supplied to the anode 12 by the pulsating force of the pulsation generator 24 has a pulsating flow force, and the water remaining in the anode 12 is moved by the pulsating flow force and discharged toward the anode outlet 16, thus improving operational stability of the fuel cell system.
In more detail, before the fuel (e.g., hydrogen) is supplied to the anode 12 of the fuel cell, the pulsation generator 24 generates a pulsating flow pressure (see FIG. 2B), (i.e., a hydrogen supply pressure) repeatedly controlled between an upper limit and a lower limit, to generate a pulsating flow force in the hydrogen supplied to the anode 12. Accordingly, the water remaining in the channel of the anode 12 of the fuel cell is moved by the pulsating flow force and discharged toward the anode outlet 16, thus improving the operational stability of the fuel cell system and increasing the purge cycle of the hydrogen purge valve for water discharge.
Therefore, when the pulsation generator is used, the discharge rate of the water remaining in the channel of the anode increases twice as much, compared to a system that does not use a pulsation generator, as shown in FIG. 3A, which prevents flooding in the anode, thus improving the operational stability of the fuel cell system.
However, there are the following drawbacks due to excessive pulsation of the pulsation generator.
First, an excessive amount of water is discharged by the excessive pulsation of the pulsation generator, and thus the water in the anode channel is reduced. That is, due to continuous generation of pulsations by the pulsation generator, the discharge of the water in the anode channel increases, which causes an excessive reduction of water in the anode channel, and thus the amount of liquid water (H2O) moved from the cathode to the anode increases, which reduces the amount of water in the cathode, thus causing dry-out in the entire fuel cell including the anode and the cathode, resulting in a reduction in the fuel cell performance and durability.
Second, since the operating pressure of the anode is continuously maintained at the pulsating pressure, the operating pressure generated in the anode increases, which increases the amount of fuel crossed over from the anode to the cathode. As a result, the fuel (e.g., hydrogen) consumption increases by about 2.5%, compared to a system that does not use a pulsation generator, as shown in FIG. 3B, which reduces the fuel utilization, and thus the efficiency of the fuel cell system is reduced by the reduction in the fuel utilization.
The above information disclosed in this section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.